Boosting a 24V diesel (or natural gas) generator set from 12V truck 2

[motorambler]

It's not uncommon to see trucks boosting (jump-starting) 12V generator sets out in the field if they have trouble starting due to cold weather, etc.

Any idea how this could be done if the generator set is 24V? I'm not interested in a scenario that would have me charging the genet's batteries individually. I want to be able to simply jump-start the genset, then move on down the road to the next one.

Thoughts?

 

[dpc]

Put two batteries in your truck connected in parallel. Then wire them in series when you want to jump the 24 V set. Many years ago a EE acquaintance had a 6V VW Beetle. He had a similar arrangement with two 6 V batteries normally in parallel. He had arranged some knife switches so he could put the batteries in series when it was extremely cold to help get his starter motor to turn the engine over. The 6V starter got pretty peppy on 12 V, as long as it wasn't left cranking very long.

If you're serious about this, there are some charging issues to consider, but it could be done - if you don't blow yourself up when switching. Or just buy a 24 V battery set and a charger and carry it in the truck. You can plug it in at night to re-charge.

 

[motorambler]

Hi dpc,

thanks for the prompt reply.

I've been asked to provide something that's "neat and unobtrusive" (my client's words). They lease the 12V trucks and vans (standard 1/2 ton and 3/4 tone domestic vehicles) and are hesitant to perform work like you suggested.

I guess I was hoping for a "magic box" solution -- one that could be clamped to the vehicle's 12V battery and also to the genset's 24V system for a quick jump-start.

 

[wayne440]

If what you want is something that can be placed in a truck in a few minutes, removed as quickly leaving little evidence that it was ever there and capable of providing near instant 24 volt cranking power to a generator - about 8K dollars will buy a Goodall Startall that produces 24V at 400A. It is powered by a gasoline engine and weighs 350lbs.

But, I bet the "client" expects this device to be hand portable, weigh 5 lbs, and cost $100. Good luck.

 

[dpc]

You can buy 12 V to 24 V dc - dc converters, but I doubt you will find one husky enough to put out the 50 to 100 A or so needed to crank a stationary engine starter.

You really need a big 24 V battery to be able to crank the engine. You could outfit the truck with a 12 V to 120 V inverter and use the 120 V ac output to run a small battery charger to recharge the 24 V battery between stops. This would all be basically off-the-shelf magic boxes.

 

[waross]

Buy two 12 Volt batteries.
Buy a series parallel switch such as is used on many older transport trucks with 12 Volt electrical systems and 24 Volt starters.
Put them all in a box and wire them up.
Buy a battery isolator such as motor homes use to charge their auxiliary batteries.
Now you can charge your battery bank from the truck electrical system.
Tip. You will need a button to activate the series parallel switch. Put it on a long cable so you can trigger the series parallel switch from the control panel of the engine that you are starting.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rmw]

Back about 30 years ago 12/24 starting was really common on large trucks, especially out west (USA) where winters were severe and cranking a cold diesel was 'iffy'. The truck electrical systems were 12 V but there was a relaying system that automatically switched two batteries to 24V for the starter circuit only when the starter was engaged. I have been out of the Tractor trailer business for some time now (thank God) so I don't know if they still offer for sale the equipment to do this or not, but if you can find some old crusty truck mechanic he/she could tell you the skinny. As batteries got better and trucks went to four and then later three batteries, I didn't see them much any more as of about the mid to late '80's.

If you could find any of the old wiring diagrams, maybe you could cobble up the parts individually and make a system. Check with Crusty. If I had a scanner here at home, I could upload some versions, but I think you can find them at a shop that has been around for a while.

Good luck.

rmw

 

[waross]

The device which allowed two twelve volt batteries to be charged and used for a 12 volt system and put in series for 24 volt starting with no ill effects on the 12 Volt system is called a series parallel switch. They are probably still available. I worked on one on my friends old Kenworth bale hauler last summer.
Out of time tonight.
I may be able to find a source for you tomorrow night.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[motorambler]

Thanks for all the input, everyone -- much appreciated. After some more discussions with the client, it turns out that modifying their vehicles is a no-go. We have to modify/revise our gensets before they take delivery so they can jump-start them from a 12V vehicle.

Gonna be ugly....

 

[catserveng]

Is your client new to this business? I had one of these on my service truck for years just for this reason,

http://www.texasindustrialelectric.com/relays_1119845.asp

Most of the gas masher and field mechanics I knew in the patch had a series parallel switch and two batteries, especially since most of the Ford diesel service trucks had two batteries anyway, wired to a connector on the front of the truck. The really slick arrangements were setup to control 12 or 24 VDC at the connector with a single switch near by.

Mike L.

 

[itsmoked]

Get another similar 12VDC battery and a marine battery box. The boxes are nice clean plastic boxes with a vented lid.

http://www.westmarine.com/webapp/wc...&subdeptNum=50543&classNum=50546#.ULb3r2dYXTo

They are made to have cables coming out of them. Get some jumper cables and cut them in half. Install battery clamps on the remaining ends and then bolt them onto the battery. You now have a 12VDC jumper battery with the cables already affixed to the battery.

When you need to jump 12V use it as-is. If you need 24VDC clamp the minus side of the jumper bat to the plus side of your vehicle battery. Hook the jumper battery's plus side to the 24V vehicle and use another half of a jumper cable to jump from your vehicle's negative side to the 24V vehicle's negative side. You're set.

Of course it takes about twice as long to read this than to actually carry out a jump-start.

To keep the jumper battery up, Occasionally just clamp it across your vehicle battery and let your vehicle idle for 10 minutes. Include some safety glasses with the battery box. You do need to bolt or strap down the jumper battery so a collision doesn't launch it somewhere bad.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

Mike,

Thanks for that link to the series/parallel switch - I didn't know those existed as a manufactured item.

dpc

 

[motorambler]

dpc's comments are echoed by us. We think we can make Mike L's solution work.

Many thanks to all that offered input.

 

[catserveng]

We used to get our service trucks from the body builders already setup, and I was just at a site in Texas where the site equipment mechanic had a brand new service truck with a series parallel switch setup. They used to jump start some equipment with a DC welder before the days of electronically controlled engines, now that is pretty much a no-no. For a while I didn't see trucks setup with the switches, then they started to show up again, I'm guessing after several electronic engines got fried ECM's the cost of a series parallel switch and a bit of wiring seemed pretty cheap.

I'll dig around and see if I can a copy of the parts list and schematic we used for our trucks, I've been away from the dealer a few years now so I'm not sure if the builder we used is even still around. I think a few of the body builders in Houston offer is a common option, at least they used too.

Hope that helps, Mike L.